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And as new research on mackerel and cod suggest, the full range of nutritients found in whole fish of all kinds may play significant roles in their health benefits.

But before we cover these intriguing new studies, let's consider the case of olive oil, which shows the pitfalls of attributing all of a food's health benefits to one nutritional factor alone.

Olive oil example supports a holistic view of foods and health

Researchers long assumed that the apparent heart benefits of olive oil flowed from its uncommon abundance of monounsaturated fats... despite a lack of lab evidence showing how they would promote cardiovascular health enough to account for the low rates of heart disease seen in Mediterranean countries.

The only difference between the two grades is that extra virgin olive oil is rich in uncommon compounds called tyrosols: potent polyphenol-type antioxidants that are utterly absent from refined olive oil.

The situation is probably reversed with fish… although omega-3s almost certainly account for most of the brain and heart health benefits associated with fish, we shouldn’t let that blind us to the possible existence of other fish-borne benefactors.

Let’s take a look at two recent studies that broaden our perspective on fish and heart health.

The first, a Spanish study involving mackerel, reminds us that you don’t need to take fish oil to enjoy cardiovascular benefits.

The second study—one from Canada, involving cod—suggests there may be something about fish protein that’s good for cardiovascular and general health.

Spanish study affirms mackerel as an artery ally

Researchers at the University Hospital in Santander, Spain assigned two groups of participants to distinctly different diets (de Berrazueta JR et al. 2008):

Group A consisted of 46 older men and women (average age 82) who agreed to eat 57 two-ounce portions of mackerel over 12 weeks (four to five portions each week).

Group B consisted of 23 seniors (13 women) who are their regular diets, without fish oil, and avoided mackerel or other fatty fish.

After 12 weeks, the performance of the participants’ arteries was measured, their pre- and post-study blood samples were analyzed, and the fish intake of Group A was confirmed with interviews.

The arteries of healthy people in Group A (mackerel eaters) was significantly improved compared to the controls in Group B.

Specifically, the mackerel-eaters’ arteries were more relaxed and open, with better blood flow, and their blood showed higher levels of anti-clotting factors associated with reduced risk of heart attack and ischemic stroke.

No changes were seen among the control subjects in Group B.

As the Spanish team wrote, “This finding might explain some of the cardio-protective effects of fish consumption” (de Berrazueta JR et al. 2008).

These findings are not so unusual, since fish oil supplements are shows to produce similar, though not identical, effects (von Schacky C 2006).

But they show that a daily fatty fish habit does arteries a world of good.

And a cardiovascular study that compared the effects of various animal protein sources suggests that some of these artery benefits may stem from factors other than omega-3s.

Cod protein cuts inflammatory heart-risk factor

Canadian researchers at Quebec’s Laval University recruited people diagnosed with a warning sign of diabetes called “insulin resistance.”

In an earlier study, they’d found that cod protein improved insulin sensitivity in insulin-resistant subjects.

They wanted to see what else cod protein might do for people experiencing this increasingly common sign of impending diabetes.

Specifically, they set out to see what impact cod protein might have on chronic low-grade inflammation, which promotes insulin resistance, diabetes, and cardiovascular disease.

The key inflammation maker doctors look for is high blood levels of C-reactive protein (CRP), which are a key risk factor for cardiovascular disease… one that rivals high cholesterol levels as a warning sign.

Accordingly, CRP blood tests have become a routine part of annual physical exams.

The Canadians recruited 19 men and women aged 40 to 65 who were overweight or obese, with insulin resistance.

Every four weeks, the subjects ate a different diet. Each diet was the same, except that each included a different protein source: cod, lean beef, pork, veal, eggs, milk, or milk products.

The diets differed only in their protein source and provided equivalent amounts of dietary fibers and each of several common dietary fats, including similar amounts of monounsaturated fat, omega-3s, and saturated fats.

Blood samples were collected before and after each experimental diet.

Only the cod protein diet decreased levels of CRP, whereas the other diets tended to increase CRP levels.

The opposite CRP impacts of the cod and other diets mean that the measured differences in CRP levels were clinically significant.

Changes in levels of other inflammation markers (interleukin-6, TNF-alpha, and adiponectin) did not differ among the diets.

As the Canadian team reported, “…these results show that [cod protein] can lower hsCRP, a marker of inflammation associated with insulin resistance and type 2 diabetes.”

We can’t know the full significance of this finding, but fish oil alone does not reduce CRP levels consistently or significantly (Balk EM et al. 2006).

Together with the mackerel study, this outcome suggests that omega-3s alone may not account for all of the cardiovascular benefits of fish.